The present invention relates to reduced nitrogen oxide (NOx) emission fuel compositions, more particularly, to high stability aqueous fuel compositions for use in internal combustion engines.
Nitrogen oxides comprise a major irritant in smog and are believed to contribute to tropospheric ozone which is a known threat to health. Environmental considerations and government regulations have increased the need to reduce NOx production. One problem with using diesel-fueled engines is that relatively high flame temperatures reached during combustion increase the tendency for the production of nitrogen oxides (NOx). These are formed from both the combination of nitrogen and oxygen in the combustion chamber and from the oxidation of organic nitrogen species in the fuel. Various methods for reducing NOx production include the use of catalytic converters, engine timing changes, exhaust recirculation, and the burning of xe2x80x9ccleanxe2x80x9d fuels. These methods are generally too expensive and/or too complicated to be placed in widespread use. The rates at which NOx are formed is related to the flame temperature. It has been shown that a small reduction in flame temperature can result in a large reduction in the production of nitrogen oxides.
One approach to lowering the flame temperature is to inject water in the combustion zone, however; this requires costly and complicated changes in engine design. An alternate method of using water to reduce flame temperature is the use of aqueous fuels, i.e., incorporating both water and fuel into an emulsion. Problems that may occur from long-term use of aqueous fuels include engine corrosion, engine wear, or precipitate deposition which may lead to engine problems and ultimately to engine inoperability. Problematic precipitate depositions include coalescing ionic species resulting in filter plugging and inorganic post combustion deposits resulting in turbo fouling. Another problem related to aqueous fuel compositions is that they often require substantial engine modifications, such as the addition of in-line homogenizers, thereby limiting their commercial utility.
A significant barrier to the commercial use of aqueous fuel emulsions is emulsion stability. Gravitational phase separation (during storage) and high temperature, high pressure/shear flow rate phase separation (in a working engine) of these emulsions has prevented successful commercialization.
The present invention addresses the problems associated with the use of aqueous fuel compositions by providing a stabile, inexpensive fuel emulsion with reduced NOX and particulate emissions.
In general, the invention features a substantially ashless fuel composition that comprises hydrocarbon petroleum distillate, purified water, and an additive composition. The fuel composition preferably is in the form of an emulsion having an average droplet diameter of less than about 10 microns, which is stable at storage temperatures, as well as, at temperatures and pressures encountered during use, such as, during recirculation in a compression ignited engine.
The process for making the emulsions greatly effects the stability of the resulting compositions. The components are mixed in a serial, continuous flow process. This process allows for the continuous monitoring and instantaneous adjustment of the flow, and thus content, of each component in the final mixture. After all components are mixed, the composition is aged prior to passing it through a shear pump. The aging time is temperature dependent. The resulting emulsion is a macro-emulsion having an average droplet size of less than about 10 microns.
The amount of the hydrocarbon petroleum distillate preferably is between about 43 weight percent and about 70 weight percent of the fuel composition, more preferably between about 63 weight percent and about 68 weight percent of the fuel composition.
The amount of purified water preferably is between about 28 weight percent and about 55 weight percent of the fuel composition, more preferably between about 30 weight percent and about 35 weight percent of the fuel composition. The purified water preferably contains no greater than about 50 parts per million calcium and magnesium ions, and no greater than about 20 parts per million silicon. More preferably, the purified water has a Total hardness of less than 10 parts per million and contains no greater than about 2 parts per million calcium and magnesium ions, and no greater than about 1 part per million silicon.
The additive composition preferably includes a surfactant and may also include one or more additives such as lubricants, corrosion inhibitors, antifreezes, ignition delay modifiers, cetane improvers, stabilizers, rheology modifiers, and the like. Individual additive ingredients may perform one or more of the aforementioned functions.